Current nuclear imaging systems are limited by poor spatial resolution, low count rate, poor photon utilization (gamma ray collection efficiency) and lack of three-dimensional capability. Improvement in any of these areas would have important clinical ramifications. Improved resolution, for example, would allow earlier detection of small filling defects and improved morphological differentiation of benign and malignant nodules. Improved quantum utilization (collection efficiency) would permit a reduction in patient dose or, if the count rate allowed, reduction in exposure time. Improved tomography could aid in the perception of low-contrast lesions. The research here is directed at each of these areas of potential improvement. Three major projects are involved, including research into gamma ray image forming elements, detection of the gamma ray image, and clinical and psychophysical evaluation of the results. Our attack on the image detector part of the problem is based on the observation that a large improvement in both resolution and count rate is possible if we limit ourselves to detectors capable of determining only one coordinate of the scintillation location. Two specific approaches to the exploitation of this dimensionality tradeoff are proposed. To fully utilize the gains afforded by either of these new detectors we need an imaging aperture that gives high resolution together with good quantum utilization, while not requiring a two-dimensional detector. Three such apertures are proposed here. An independent study, applicable to many different apertures, will investigate study, applicable different apertures, will investigate the possibility of deriving a two-dimensional transverse section (CT) from a one-dimensional coded image. Another primary thrust of this effort is a systematic and continuing program of image evaluation. Based on both clinical and psychophysical methods, this project will both guide and evaluate the instrumentation efforts. Major questions that it will address include the usefulness of tomography of various sorts and the subjective performance of our new imaging systems.